1. Field of the Invention
Apparatuses, methods and systems consistent with the present invention relate to a transmitting/receiving data coded by a low density parity check matrix code, and more particularly, to transmitting/receiving data coded by a low density parity check matrix code for providing various code rates and superior performance.
2. Description of the Related Art
A cellular mode mobile telecommunication system was introduced in the United States in the late 1970's and an advanced mobile phone service (AMPS) was provided as a voice wireless communication service in Korea in the late 1980's. The advanced mobile phone service is an analog mode of a 1st generation mobile communication system (1G). Subsequently, a 2nd generation mobile communication system was commercialized in the mid 1990's and a part of International Mobile Telecommunication-2000 (IMT-2000) standard was commercialized in late 1990's as a 3rd generation mobile communication system for providing improved and high speed wireless multimedia data service.
Recently, there are many studies in progress for developing the 3rd generation mobile communication system into a 4th generation mobile communication system (4G). The 4th generation mobile communication system has been developed to achieve objects such as effective connection between a wired communication network and a wireless communication, and an integrated service. Therefore, various specifications of the 4th generation mobile communication system have been standardized for developing technologies providing faster data transmission service as compared to the 3rd mobile communication system.
Meanwhile, the most fundamental problem in communication is how to transmit data effectively and reliably through a channel. The next generation mobile communication requires a high speed communication system processing various information such as voice, image and data, and transmitting the processed information at high speed. Accordingly, an effective channel coding scheme is required for improving efficiency of the communication system.
Furthermore, rapid development of the mobile communication system has led to the need to develop a technology for transmitting large amounts of data in wireless networks comparable to wired networks. Therefore, increasing data transmission efficiency has become a major factor for improving a performance of the communication system. However, the mobile communication system may have difficulty transmitting large amounts of data at high speed due to unavoidable errors such as noise, interference and fading caused by channel conditions during data transmission. Accordingly, information data is often lost due to the errors.
For reducing information data loss caused by the error, various error-control techniques have been introduced and widely applied according to a characteristic of a channel. The various error-control techniques have increased the reliability of the mobile communication system. Among the various error-control techniques, an error-correcting code has been commonly used. Representative error-control techniques include a turbo code and a low density parity check (LDPC).
Meanwhile, the above mentioned channel coding is an essential constitutional element of a MODEM in a multiband orthogonal frequency division multiplexing (OFDM) system which is used in a wireless personal area network system.
FIG. 1 is a block diagram illustrating a conventional multiband OFDM system using convolution coder.
As shown in FIG. 1, the conventional multiband OFDM system includes a transmitting unit and a receiving unit. The transmitting unit includes a scrambler 110, a convolution encoder 111, a puncturer 112, a bit interleaver 113, a constellation mapper 114, an inverse fast fourier transform (IFFT) unit 115, a digital-to-analog (D/A) converter 116, a multiplier 117 and an antenna 118. The scrambler 110 receives and scrambles input data. The convolution encoder 111 encodes the scrambled data from the scrambler 110. The puncturer 112 punctures the encoded data from the convolution encoder 111 according to a code rate of data to be transmitted.
The bit interleaver 113 interleaves a bit to the punctured data and the constellation mapper 114 converts the bit-interleaved data to corresponding symbols. The IFFT unit 115 performs IFFT of the symbols and the transformed symbols are converted to analog signal by the D/A converter 116. The analog signal is multiplied with a carrier frequency ex(j2πfct) by the multiplier 117 and the multiplied analog signal is transmitted to the receiving unit through the antenna 118.
The receiving unit of the multiband OFDM system includes a descrambler 120, an decoder 121, a de-puncturer 122, a de-interleaver 123, an FFT unit 124, two A/D converters 125a, 125b, two multipliers 126a, 126b, a low noise amplifier (LNA) 127, and an antenna 128. The LNA 127 receives a signal transmitted from the transmitting unit through the antenna 128 and amplifies the received signal. The two multipliers 126a and 126b divide the received signal into an I-channel signal and a Q-channel signal and the A/D converters 125a and 125b convert the I-channel signal and the Q-channel signal to digital signals.
The digital signal is fast-fourier transformed by the FFT unit 124 and the transformed digital signal is de-interleaved by the de-interleaver 123. The de-puncturer 122 inserts bits for each of the punctured bits. The bit inserted digital signal is decoded by the decoder 121 i.e., a viterbi decoder. Finally, the de-scrambler 120 de-scrambles the decoded signal for generating a final output data.
As mentioned above, the multiband OFDM system essentially requires an encoding operation and additional requires puncturing operation for puncturing the encoded data according to corresponding code rate in the transmitting unit.
The convolution encoder has been commonly used as the encoder for supporting various code rates. However, the convolution encoder has degraded bit error rate (BER) performance as compared to the LDPC encoder.
FIG. 2 is a graph showing a performance difference between a convolution coding and an LDPC coding.
Referring to FIG. 2, the graph shows packet error rates (PER) of an original signal 201, convolution coded signals 202, 203, 204 and LDPC coded signals 205, 206 and 207. The convolution coded signals 202, 203, 204 are encoded and interleaved based on the convolution encoding and have a code rate of ½, ⅝ and ¾, respectively. The LDPC coded signals 205, 206 and 207 are encoded based on the LDPC encoding and have a code rate of ½, ⅝ and ¾, respectively. According to the graph, there is a performance difference of about 6.8 dB between the convolution coded signals and the LDPC coded signals.
Therefore, the LDPC encoding has been considered as an encoding scheme for the next generation mobile communication system. However, the LDPC encoding scheme requires performing puncturing according to code rates when the LDPC encoding scheme is applied to the next generation mobile communication system supporting various code rates. If a random puncturing method is used in the LDPC encoding scheme as a method for puncturing, the performance would be degraded. Therefore, although the LDPC encoding scheme provides superior coding performance, there are difficulties in applying the LDPC encoding scheme to the mobile communication system supporting various code rates.
In order to overcome the above mentioned problem, a method using a plurality of mother codes according to corresponding code rate without puncturing the LDPC code in an Infineon has been introduced as encoding scheme for supporting various code rates without degradation of performance while using the LDPC coding scheme. This method improves performance as compared to the convolution encoding scheme. However, the method results in increased complexity because additional mother codes are required according to each code rate.
Therefore, there has been great demand for an encoding scheme having lower complexity and superior performance in a mobile communication system supporting various code rates.